This invention concerns an airjet weaving machine with an improved supply for the weft threads.
It is known that the supply for weft threads on an airjet weaving machine normally consists of several thread preparation mechanisms, each made up of at least one yarn package, a thread accumulator such as for example a prewinder device, a thread blocking mechanism in order to release suitable lengths of weft thread from the prewinder device, and a main nozzle.
It is clear that the different thread preparation mechanisms can operate with different weft threads, for example in order to weave with several colours.
From Belgian patent No. 901.969 it is known for the thread preparation mechanism to be duplicated. For each thread preparation mechanism there is a thread detector connected to a control unit, such that whenever a broken weft thread is detected in a thread preparation mechanism, the system switches over automatically to the other thread preparation mechanism, so that weaving can continue without interruption.
The main nozzle of the deactivated thread preparation mechanism, however, remains activated, normally at a low rate of flow, so that the length of weft thread between the thread blocking mechanism and the main nozzle remains taut. If this were not the case, the length of weft thread would fall out of the main nozzle and become entangled in the other weft threads.
Whenever a thread preparation mechanism is placed on standby, the weaver must intervene in order to repair the defective supply channel. However, it may happen that the above-mentioned length of weft thread has to wait too long in a main nozzle. The main nozzle is normally mounted on the sley of the weaving machine, and thus carries out a back-and-forth movement, with the result that the length of weft thread extending into the main nozzle is heavily stressed and can break.
If the length of weft thread breaks close to the main nozzle placed on standby, the piece of thread which comes loose may be blown into the shed along with a weft thread from another main nozzle, giving rise to a weaving fault which can greatly reduce the quality of the cloth.
If the above-mentioned weft thread breaks close to the thread accumulator, there is a great chance of the broken-off piece of thread becoming entangled with the other weft threads, and thus either being blown together with them into the shed via another main nozzle or blocking the other main nozzles. In the latter case a weaving machine stop occurs which can last relatively long, since the weaver is usually not in a position to attend to the stoppage immediately.